1. Field of the Invention
The present invention relates to a wheel which is made from steel and is constructed by welding separate members of a disk and a rim (hereinafter, a two-piece wheel).
2. Description of Related Art
Automobile wheels are generally divided into two types: one is a two-piece wheel made from steel or aluminum and the other is an integral casted or forged wheel made from aluminum. The objective wheel of the present invention is the two-piece wheel made from steel.
The conventional two-piece steel wheels have been constructed, as illustrated in FIG. 4, by fitting a radially outer portion 2a of a disk 2 to an inside surface of a rim 1 having two rim flanges 1a. However, since the fitted line of the wheel can be seen from an outboard side of the wheel, thereby degrading its appearance, an integral design type of wheel as illustrated in FIG. 3 has been proposed in U.S. Pat. No. 4,610,482 to solve such problems. The radially outer portion of the wheel 3 has the same shape of a rim flange, and the rim 4 has a rim flange 4a at one end and a rim bead seat 4b at the other end. The rim bead seat 4b at the other end has a radially inwardly extending flange 4c and the rim is welded to the disk of the wheel 3 at the bent portion of the rim bead scat 4b.
However, with the wheel there are still the problems that the number of forming, steps is increased by the step of forming the flange 4c, that the weight of the wheel is increased by the flange 4c, and that the decoration holes should be provided radially inside the flange 4c. Consequently, the effect of the integral design that makes the outboard surface of the wheel look broad is decreased.
To solve such problems, the inventors of the present application have proposed a two-piece steel wheel in Japanese Patent Publication No. HEI 9-20103, as illustrated in FIG. 2. In the wheel, the radially outer portion 5a of the disk 5 which is formed in the shape of a rim flange is machined so as to provide a stepped portion 5b. A straightly extending rim bead seat 6a of the rim 6 is fitted to the stepped portion 5b and an end surface 6b is abutted to the machined inboard surface of the radially outer portion 5a of the disk 5, and, while maintaining that state, the rim 6 and the disk 5 arc welded together from radially outside of the rim 6.
However, with the wheel of FIG. 2, there are still the following problems:
(1) Since the disk has the stepped portion 5b, a stress concentrates at the stepped portion 5b. To endure the concentrated stress, the thickness of the disk has to be increased. PA0 (2) Water and/or mud enter the weld to cause rust through a small gap between the end surface 6b of the rim and the machined surface of the disk 5. To prevent rust, a particular penetration weld has to be developed, which increases the welding cost. PA0 (3) Since the inside surface of the rim bead seat 6a is fitted to the stepped portion 5b of the disk 5, fitting of a relatively higch precision is required, which increases the machining cost.